Vapor generation and superheating



May 23, 1961 Filed June 25, 1954 P. S. DICKEY VAPOR GENERATION AND SUPERHEATING 7 Sheets-Sheet l w HP ,D X

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VAPOR GENERATION AND SUPERHEATING Filed June 25, 1954' 7 Sheets-Sheet 2 37-l AF GAS TEMP.- F

TERTIARY AIR j PRIMARY AIR J a 48-! 43 GAS FLOW PATH I I FIG. 4 B

COAL

CYCLONES MIXING CHAMBER 4 SECONDARY MIXING CHAMBER CYCLONE TYPE F NACE FIG. 2 INVENTOR.

PAUL S. DICKEY BY ATTORN May 23, 1961 Filed June 25, 1954 ILOAD INDEX P. S. DICKEY VAPOR GENERATION AND SUPERHEATING 7 Sheets-Sheet 3 I60 I I TURBINE FEEDWATER CYOLONES I STAGE FLOW 25-3 25-I I PRESSURE TOTAL l T T T T MASS RECIROULATION I GAS FLOW GAS FLOW OXYGEN LI 37-3 37-2 I GF2 SP3 I GFI [3 AIR FLOW SUPPLY 30 I 32 i I l I I l l l l l I I I I I I I I I I Pl P2 P4 P5 7 TI T2 T3 T4 T5 T6 T7 GTI GT2 T8 T9 TIO GAS TEMP.

I I MANUAL CONTROL STATION |6I II I I I I I I I I I I l I I l O O 0 0 O O C O I O O I O O I O O I {2 a: l I I I 2} I 26 Z 2 ;3- i 2 -51 1 I 47-3 47-2 47-l I I I 7 l I M M M M M M M M M M M I M FEED FORCED DISTRIBUTION RECIR COMBUSTION AIR FUEL FEEDERS PUMPS DRAFT DAMPERS FAN CYCLONE FURNACES FAN I2 FIG. 3

INVENTOR. PAUL S. DICKEY ATTORN May 23, 1961 P. s. DICKEY VAPOR GENERATION AND SUPERHEATING 7 Sheets-Sheet 5 Filed June 25, 1954 INVENTOR.

PAUL S. DICKEY P. s. DICKEY 2,984,984

VAPOR GENERATION AND SUPERHEATING 7 Sheets-Sheet 7 INVENTOR.

PAUL S. DICKEY A RNEY mO2mm Oo mmowwmma May 23, 1961 Filed June 25, 1954 :1 Q25 mm. 03

@2 Q Ewsim 561 mm 502mm 5 Etiwzflt 5mm od 5 5 E2;

mHFrOmIk United States Patent VAPOR GENERATION AND SUPERHEATING Paul S. Dickey, East Cleveland, Ohio, assignor to Bailey Meter Company, a corporation of Delaware Filed June 25, 1954, Ser. No. 439,185

22 Claims. (Cl. 69-73) This invention relates to forced-flow once-through vapor generators of the universal pressure type, i.e. arranged for operation at pressures either above or below the critical pressure of 3206 p.s.i. I am particularly concerned with providing method and apparatus for controlling the operation of such a unit to maintain efiicient generation and supcrheating of the working medium to a desired final fluid temperature and pressure while satisfying load demands.

While I will disclose and describe my invention preferably in connection with above-critical operation, it will be apparent that the method and apparatus of control is equally applicable to operation of the unit at belowcritical pressures.

Forced-flow once-through units for operation at above the critical have been proposed but to my knowledge have not previously been commercially operated; one reason being the lack of a feasible method and apparatus for control based upon an adequate appreciation of the problems and a satisfactory solution thereof. Such units are formed with tube paths for the working medium, with liquid under high pressure supplied at one end and superheated vapor or working medium discharged from the other end to a turbine or other point of usage.

The tubular heating path for the Working medium may consist of a plurality of parallel long small-bore tubes with no drums or other enlargements and thus adapted to contain fluid at higher pressure than would otherwise be possible. The tubular path is arranged to be contacted by the products of combustion and heating gases, with some portions subjected to radiant heating and other portions to convection heating.

The exemplary unit to which the present invention is particularly directed, and in connection with which it will be described, is arranged to receive feedwater at a pressure of 5500 p.s.i. and a temperature of 515 F. and to discharge working fluid at 4500 p.s.i. and 1150 F. As the entire heating is above the critical pressure of 3206 p.s.i. there is little density difference of the fluid throughout the path and, while the nature of the final superheated fluid is not actually known, it may conveniently be called steam. Double reheat is employed. Thus, superheated steam at 4500 p.s.i. and 1150 F. is supplied to a high pressure turbine from which the exhaust steam is returned to a high pressure reheat surface in the unit where the steam is reheated at approximately 1150 p.s.i. to a temperature of 1050 F. and is then passed to a low pressure reheat turbine section. Steam leaving the first reheat turbine at approximately 630 F. is returned to a low pressure reheat surface of the unit, leaving at 165 p.s.i. and 1000 F. to a low pressure turbine discharging to a condenser or heater system. Thus the fluid heating unit includes primary fluid heating and superheating surfaces as well as two reheat sections of convection heating surfaces.

Feedwater, as well as fuel and air for combustion, must be supplied at the proper rates and proportions to heat the primary working fluid and the reheat flows to maintain optimum outlet temperatures and pressures. I have found that the problems of control encountered at abovecritical pressure operation indicate that prior control methods and apparatus, for units operating below the critical, are not satisfactory here.

Pressure in the steam generator will be controlled sole 1y by the discharge pressure of the feed pumps. A pressure regulator at the turbine throttle will therefore control pump speed rather than firing rate as in other installations. Heat input to the unit will be controlled primarily in accordance With main steam flow and temperature. Temperatures'at the two reheat points will be controlled by the interaction of dampers in the gas passes leaving the reheater and superheater surfaces. The control valves at the turbine will be throttling valves to vary load on the machine by varying steam pressure to the first stage. Various features in the control of the generating and superheating unit as well as of the utilization apparatus, are embodied in the methods and apparatus of my present invention.

A principal object of my invention is, therefore, to provide method and apparatus for control of a universal pressure forced-flow once-through vapor generator capable of operating at conditions either above or below the critical.

Another object is to control the supply rate of the working medium, as well as the rate of supply and distribution of heating gases over fixed heating surfaces, of an above-critical pressure unit, to maintain optimum pressure and temperature conditions of the fluid leaving the unit.

A further object is to provide method and apparatus for control of a fluid heating and/ or vapor generating and utilizing station including what may be termed a vapor generator, as well as a plurality of turbines utilizing superheated vapor, with vapor reheating provisions in the vapor generator.

Still another object is to provide method of operation and apparatus for control of a thermal power station utilizing superheated working medium in a first turbine, returning the medium to be reheated, and passing the reheated medium through one or more other turbines.

An object of the invention is to provide method and apparatus to control the turbine or turbines of such a thermal power station.

Still another object is to provide a control of turbine cooling steam.

Other objects will become evident from a consideration of the drawings and of the description in connection therewith.

In the drawings:

Fig. 1 is a diagrammatic representation of the flow path of the working medium as well as the flow path of the heating gases, of a forced-flow once-through unit operable either above or below the critical.

Fig. 2 is a somewhat diagrammatic sectional elevation of a cyclone type furnace for the unit.

Fig. 3 illustrates a measurement and control panel particularly useful in performing the methods of the invention.

Fig. 4 is a schematic control diagram illustrating the measuring and controlling apparatus arranged to automatically regulate the supply of feed water and the elements of combustion responsive to selected variables in unit operation.

Fig. 4A is an extension of Fig. 4, being a control diagram illustrating measuring and controlling apparatus arranged to automatically regulate the rate of recirculation of partially cooled heating gases to the furnace.

Fig. 4B is a graph of characteristic gas temperatures progressively through the gas flow path.

Fig. 5 is a control diagram for the regulation of induced draft fans for the unit.

Fig. 6 is a control diagram for automatically regulating the heating gas distribution over a plurality of convection heating surfaces.

Fig. 7 is a line diagram of the working fiuid cycle including the generating-superheating unit as well as the various turbines of the example.

Fig. 8 is a more detailed control diagram of turbine pressure control of Fig. 7.

Fig. 9 is a more detailed control diagram of turbine cooling steam control of Fig. 7.

Referring now to Fig. 1 I show therein, in quite diagrammatic manner, the flow path of the working fluid and of the heating gases. Three cyclone type furnaces 1 2-3 are separately supplied with the elements of combustion and discharge to a common mixing chamber 4 under high velocity the gaseous products of combustion at a temperature of the order of 3000 F. or higher which is high enough so that a major portion of the fuel ash is discharged as molten slag either directly from the cyclones or from the mixing chamber. The mixing chamber 4 is enclosed by radiant walls 5 formed of a portion of the tube passage. Having thus disposed of the major portion of the ash, it is desirable to immediately reduce the heating gas temperature to the order of 1900 F., below the ash fusing value, so that any remaining ash will not stick to and plug the small closely-spaced convection tube surfaces. Tempering of the gaseous products of combustion in the mixing chamber is accomplished by recirculating partially cooled heating gases thereto under controllable conditions. The tempered heating gases then pass successively over the secondary superheating surface 6 and are proportioned thereafter as between the primary superheater 7 and the reheat surfaces 8, 9 to the air heater. Partially cooled heating gases are recirculated from the outlet duct'ltl. through a return duct 11, by one or more recirculating fans 12, to enter the mixing chamber at preselected location. Reference to Fig. 4B shows a typical expected temperature gradient for the gas fiow path. Temperates of some 3100 F. are expected at the exit of the cyclones into the mixing chamber. Tempering of the gases immediately drops the temperature to approximately 1900 F. from which there is a gradual decrease through the convection heating surfaces to some 800 F. at the entrance to the air heater.

Feedwater enters the tubular heating passage at 13 from a pair of high pressure feedwater pumps 14, 15 under flow control, and passes serially around the cyclones 12-3 and through a conduit 16 to the primary superheater 7. The Working fluid then traverses the primary superheater, radiant wall section 5, and secondary superheater 5, successively, leaving the unit through a conduit 17 to the high pressure turbine 18 for producing useful work. 7 A portion of the steam from conduit 17 is used as cooling steam for the high pressure turbine under a control to be explained.

It will be appreciated that, while I illustrate in Fig. 1 a single tube passage for the working medium, the passage actually comprises a plurality of parallel small-bore tubes and there may be more tubes in parallel in one section of the heating surface than in another.

Steam leaving the high pressure turbine 18 passes successively through the high pressure reheater convection surface 8, a high pressure reheat turbine 19, the low pressure reheat convection surface 9, and the low pressure reheat turbine 20, to, the low pressure turbine 21 from which it discharges to a condenser 22. Stage bleeding from the turbines and feedwater heating apparatus are not shown nor are various shut-off valves, safety valves, and the like. At 23 I show a conduit joining the outlet of primary superheater 7 with the condenser 22, or other feedwater preparation apparatus, to constitute a bypass for the radiant superheater 5 and the secondary superheater 6, under certain emergency and start-up conditions. Positioned in the conduit 23 is a valve 24 which may be 4 manually or remotely manually actuated, or, in certain instances, may be automatically positioned.

Pressure and temperature responsive meters are located at indicated points along the path of the working medium as shown on Fig. 1. Wherever, hereafter, I indicate a pressure value for P2 (for example) or a temperature value for T2 (for example) I mean the pressure or temperature existing in the conduit 17 at the locations P2 or T2 as shown in Fig. 1. By way of example the following set of pressure and temperature values may exist under normal operation of the unit.

1 (Varies with load.)

At rated load the expected steam flow rate is:

675,000 lb. per hr. at location P2 615,000 lb. per hr. at location P4 525,000 lb. per hr. at location P6 The values of pressure and temperature given above are the expected values at rated load (for this particular example). and it is not particularly material as to the values of P7 and T7 as stage bleeding will vary these values. The temperature measuring locations T8, T9, T10 are exploratory and the expected values will lie betv een the values T1 and T2. These locations T8, T9,

10 are in What, for Want of a better name, may be termed the transition zone or intermediate zone. In above-critical pressure operation there is a smooth transition from what may be termed water to that which may be termed steam. The density of the two is approximately the same and there is no latent heat of vaporization. The tubular passage is designed and located for heating to allow a gradual increase in temperature of the Working medium from T1 to T2. Somelocation along the path as T8 or T9 or T10, however, provides'an operational index for the controls, more sensitive in anticipating changes in T2 than is a measure of T2 itself. It is thus utilized in my preferred control system as an anticipatory effect.

The use of transition zone temperature in the control of the unit, either manually or automatically, tends to earlier show unbalance between Water supply rate and heat supply rate because there is of course some lag in the response of T2 to variations in input water supply rate and input of the elements of combustion. The closer to the outlet T2 that the intermediate zone temperature T8 or T9 or T10 is taken, the slower the response therefrom, although the value of the selected intermediate zone temperature is closer to the actual temperature T2. Variations in T8, T9 or T10 will tend to show a shift of the transition or intermediate zone along the tubular path and this becomes of even more importance when operating the unit below critical pressure because in that instance itfollows pressure. Transition zone is a term used in below=critical pressure units for the location of transition between liquid and vapor and will clearly show the movement of the transition zone along the path and thus the proportioning of the path between liquid and vapor. It is somewhat of a misnomer in connection with above-critical operation. In above-critical pressure operation, the transition or intermediate zone temperature which is used in the guiding of operation is selected as an anticipatory control, somewhat in advance of variations in the value T2 which may be caused by variations in the rate of supply of feedwater or of the elements of combustion.

Fig. 1 shows the location of other instrumentalities for measuring variables in the operation of the unit, useful for either manual or automatic control thereof. In connection with the cyclone furnace 1 I show an oxygen determining gas analyzer designated as 25-1 and, on Fig. 3, I designate the similar gas analyzers for cyclones 2 and 3 as 25-2 and 25-3. These oxygen analyzers are connected to be sensitive to the gaseous products of combustion leaving the individual cyclone furnaces at their entrance to the mixing chamber 4 and are useful in controlling the proportioning of the elements of combustion to the individual cyclones.

For feedwater supply I show two high pressure pumps 14, 15 provided with speed control mechanisms 26, 27 respectively and discharging to the conduit 13. A rateof-fiow meter 28-1 is provided in connection with pump 14 and a similar flow meter 28-2 is provided in connection with pump 15.

Located in the duct 11 is an orifice 29 for a gas flow meter 30 which continuously measures the gas recirculated by the fan 12 to the mixing chamber 4. It will be understood that the necessary dampers are provided in connection with the duct 11 on either or both sides of the fan 12 and may be used for control purposes. Control is, however, in this example, through the regulation of speed of the recirculating fan (or fans) 12 and through the agency of a control device 31 which may be an electric motor or a pneumatic operator.

Temperature of the gaseous products of combustion leaving the mixing chamber 4, as tempered by the recirculated gases, has an expected value at location GT1 of approximately 1900 F. I show another point of gas temperature measurement GT2 following the secondary superheater 6 at the entrance of the primary superheater and reheaters. It is not possible to exactly predict the temperature at GT2 but it will be somewhat lower than 1900 F. (in the neighborhood of 1400 F.) and is used in my preferred method and control apparatus as indicative of operating conditions. The exact value of GT2 is not particularly important. What is important, is that a measureable gas temperature approximately midway along the gradual decrease slope (1900 F.800 F. of Fig. 4B) is indicative of changes in heat availability and heat utilization, without the necessity or difficulty of accurate measurement of the higher value 1900 F., nor experiencing the time lag through utilizing a measurement of the lower value around 800 F. Some intermediate point, readily and accurately measurable, is commercially satisfactory as giving a reflected value of temperature changes at the high end (2000 F. to 1900 P.) where it is quite difficult to obtain continuous and accurate temperature measurements.

The total mass flow of heating gases leaving the mixing chamber 4, and passing over the superheating and reheating surfaces, is made up of the fresh products of combustion and excess air, as well as the recirculated gases. It is quite desirable to ascertain the flow rate of the total heating gases and I accomplish this by continuously ascertaining the pressure drop GFl-GFZ and adding this (in terms of flow rate) to the pressure drop GF1-GF3, to give a summation of the flow rate of gases passing through the secondary superheater and as distributed between the primary superheater and the reheater surfaces. Referring to Fig. 3 the total mass gas flow meter 32 is sensitive to the values GF2, GFl, GF3 and records total mass gas fiow, giving an instantaneous indication and a permanent record thereof. It also may advise the flow rate values GFl-GFZ and GF1-GF3 individually. Indicating instruments 33 and 34 continuously indicate the values GT1 and GT2 as a guide for remote manual control of the unit.

Heating gases passing over the convection surfaces are distributed, as between the primary superheater 7 and the reheater surfaces 8, 9, by distribution dampers 38, 39 which may be remotely manually positioned or positioned through automatic control means.

Fuel and air are supplied for combustion to the three cyclone furnaces in a manner which will be explained more in detail in connection with Fig. 2. In Fig. 1, however, I have indicated a main duct 35 for supplying the combustion air to all three of the cyclones. Primary air and fuel are supplied to the individual cyclones through pipes designated 36-1, 36-2 and 36-3. In the three branch ducts, under control of the dampers 35-1, 35-2 and 35-3, I provide individual orifices and an air flow meter in connection with each orifice. I have shown at 37-1 the air flow meter for that air branch supplying cyclone furance -1.

It will be seen then that, in Fig. 1 I show measuring instrumentalities and controllable devices by which the unit may be remotely manually or automatically regulated.

Referring now to Fig. 2 it will be seen that I have illustrated therein, in sectional elevation, the cyclone furnace 1 discharging into the mixing chamber 4, and in connection therewith I have shown the necessary fresh air supply from duct 35. I also illustrate, in diagrammatic fashion, the coal supply, feeder, crusher, and control dampers in connection with this particular cyclone. I show the said elements in functional relationship to the unit rather than in actual physical interrelation because the latter would add nothing to an understanding of my invention. It will be understood that the air supply duct 35 leads from a forced draft fan (not shown) and at the same time, in similar manner, supplies the cyclone furnaces 2 and 3. Thus the arrangement of Fig. 2 is representative of each of the three cyclone furnaces.

Cyclone furnace 1 is actually a primary furnace in which the elements of combustion combine and discharge the resulting products of combustion to the mixing chamber 4 which is common to all three of the cyclones. Crushed coal is admitted through a pipe 36-1 tangentially to the burner portion 42 in a stream of primary air under control of a damper 43 at sufiiciently high velocity so that particles of coal will be thrown toward the interior surface of the cylinder 44 and will be carried in the air stream along the wall of the cylinder in the form of an increasing-pitch helix until the energy of the entering stream of air has been dissipated. In addition to the primary air, sufficient secondary air for complete combustion of the coal is admitted from the duct 35 in a path parallel to the primary air and coal with corresponding high velocity and under control of the damper 35-1. As the fusing temperature of the ash is usually lower than the temperature obtained from combustion, the ash will be in a molten state as slag, and, due to the energy in the stream of products of combustion, will be in contact with the inner surface of the cyclone furnace so that the latter becomes entirely coated with molten or sticky slag.

The axis of the furnace 1 may be horizontal or inclined slightly and the molten slag may be continuously tapped as at 45. As the molten slag inner-surface of the burner is established it will act like fiy-paper to trap crushed coal admitted with the primary air and then thrown to the surface of the burner by the energy of the air. The movement of the slag along the surface of the burner, due to its viscosity, is very much less than 7 the velocity of the entering air and this provides an intense scrubbing action of the high velocity air on the coal particles which are entrapped by and moving with the slower moving film of molten slag with a resulting extremely high combustion rate. The cylinder 44 may be surrounded by closely spaced tube coils, as shown in Fig. l, supplied with feedwater from the conduit 13, and serially connected to enwrap the furnaces 1, 2, 3 successively, with exit to the conduit 16. The fuel and air supply to one or more of the cyclones may be discontinued without affecting the flow of water from the conduit 13, but only the supply of heat to the water in the tubes surrounding the cut oif cyclone.

In general, substantially complete combustion occurs within the cyclone burner which discharges flame and products of combustion into the mim'ng chamber 4. Normal commercial operation occurs at about 10% excess air. Substantially all of the ash from the burning fuel remains in molten form within the cylinder 44 and thus the heating gases passing into and through the mixing chamber are substantially clean and free of fly-ash, unburned carbon and the like. A certain amount of fly ash will however be carried from the mixing chamber toward the convection heating surfaces and, to prevent adhesion and plugging of these closely spaced small tube surfaces, I preferably temper the gases by recirculation of partially cooled heating gases as previously mentioned.

Normal air distribution'may be in the order of 10-15% as primary air, 58% as tertiary, and the remainder as secondary air. The flow quantities of primary and tertiary air do not vary greatly with rating and are usually adjusted manually by dampers 43 and 43A.

Coal is fed through a feeder 46 which is driven by an adjustable speed motor 47--1 under the control of a rheostat 48-1. The coal passes through a crusher 49, to which primary air is admitted under control of damper 43, discharging to the duct 361 a mixture of primary carrier air and crushed coal which may have particles up to to A2. The extremely high rate of combustion within a cyclone type furnace is carried on with a minimum of excess air and it is importantto ascertain just what the free oxygen content is of the gaseous products of combustion discharged to the mixing chamber 4. Thus a sampling tube 25-1 is indicated for continuously ascertaining the percentage in the gases discharged from the cyclone.

Final steam temperature is controlled primarily by controlling the firing rate of the cyclones to vary the quantity of high temperature heating gases to the radiant and convection surfaces. At partial loads the final temperatures may be increased by manually removing the fire of one cyclone to lower the heat absorption of the water and this is possible by the series flow arrangement of the water around the three cyclones.

Stopping the firing of one cyclone presumably removes one third of the heat supply rate to the unit, unless there is a simultaneous equivalent increase in fuel and air supply rate to the two remaining cyclones, preferably equally divided therebetween. Such provisions are available as described and claimed in the patent to Jack E. Wilhelm No. 2,745,603 dated May 15, 1956.

Refer now to the automatic control system shown quite diagrammatically in Figs. 4, 4A, 5 and 6. Progressing across these figuresfrom left to right it will be seen that I first illustrate a preferred control of feedwater supply rate, next forced draft fan control, then control of fuel and air to the cyclones, control of recirculation fan speed, induced draft fan speed, and reheater outlet steam temperature. The designations and numerals agree with those applied to the measuring instrumentalities and controlled devicesof'Figs. 1, 2 and 3.

The basic concept and control of this unit is somewhat different than for other installations. I regulate feedwater supply rate to maintain final steam pressure. A pressure regulator at-the turbine throttle will therefore control pump speed rather than firing rate as in other installations. With the very little change in density throughout the length of the flow path for operation above the critical, the fluid acts somewhat as a pushingstick wherein an increase in flow rate or pressure at the input point reacts all the way through the tube passage to the outlet pressure. There is no buffer zone such as a separation drum or compressible steam passage and thus pressure throughout the unit can be controlled by the discharge pressure of the feed pumps.

Heat input to the unit will be controlled primarily in accordance with main steam flow (or some indication thereof-such as total water flow), final superheated steam temperature, and an intermediate zone temperature.

Final temperatures of the two reheat flows will be controlled by the damper proportioning of heating gases over the superheating and reheating surfaces; as well as by attemperation.

Considering first the control of feedwater supply rate by boiler feed pump control, with the diagram of Fig. 4, there are two basic modes of boiler-turbine operation contemplated.

The boiler feed pump control is arranged so that it may be operated as a simple flow control to maintain a constant predetermined flow rate. It can also be used as a pressure control where the pump flow is varied to maintain a constant pressure at the turbine inlet.

The first is a block loading that cannot change except under an emergency condition. This would be a simple flow control to maintain a constant, predetermined flow rate of water through the conduit 13.

Throttle pressure P2 (Fig. l) is effective within a transmitter 50 which may be of the type disclosed and claimed in the Gorrie Patent No. 2,737,963 dated March 13, 1956 establishing in a pipe 51 a fluid loading pressure continuously representative of turbine throttle pressure. As an indication of turbine load I utilize the high pressure turbine stage pressure L1 (Fig. 1), effective within a transmitter 52 which is similar to transmitter 50, to establish in a pipe 53 a fluid loading pressure continuously representative of load or demand.

Pipe 51 joins the A chamber of reset or standardizing relay 54 which may be similar to the relay of the patent to Gorrie No. 2,776,669 dated January 8, 1957 and providing an output control pressure in a pipe 55.

Pipe '55 joins the A chamber, and pipe 53 joins the B chamber, of an averaging relay 56, producing a resultant control pressure in pipe 57 which is effective upon the A chamber of a relay 58 by way of a manual-automatic selector station 59. Output of the relay 58 is efiective within the A chamber of a standardizing relay 60.

Feedwater flow meter 28-1 comprises a transmitter establishing in a pipe 61 a fluid loading pressure continuously representative of feedwater rate supplied to the conduit 13 by the pump 14. This transmitter may be like the Gorrie, Patent No. 2,737,963 and similar to transmitters 51, 52. Transmitter 28-2 is similar to 28-1 and establishes in a pipe 62 a fluid loading pressure continuously representative of feedwater flow rate supplied to the conduit 13 by the pump 15.

While I have shown the transmitters 50 and 28P1 in some detail, and have referred to the more complete disclosure of certain patents, I have, for simplicity, indicated the various other transmitters of my control circuits by block diagram. It will be appreciated that measuring transmitters such as T2, L1, 25-1, etc, are similar in construction and operation to the transmitters 50 and 28-4 in establishing a fluid loading pressure (in this instance a pneumatic loading) in a range such as 3-27 p.s.i.g. continuously representative of the value of the variable being measured and which is to be transmitted. In similar manner I have somewhat detailed the standardizing relay 54 but have shown the remaining relays of the control diagram in simple block fashion. The relay 54"has an adjustable restriction or bleed 63 from the output or D chamber pressure into a balancing C chamber. All of the other block diagram relays of the control circuits are provided with A, B, C, D chambers, some or all of which may be utilized. Wherever one of the relays is of the reset or standardizing type I have illustrated it as having an adjustable restriction between the C and D chambers similar to relay 54.

Relay 64 is a totalizing relay receptive of the loading pressures of pipes 61 and 62 and producing a control pressure in pipes 65 and 66 representative of total water flow rate supplied to the conduit 13. Pipe 65 joins a low-flow unit trip 67 as an emergency or safety feature. Pipe 65 also joins the B chamber of standardizing relay 60 whose A chamber is receptive of the output of relay 58. The output of relay 60, in pipe 68, divides and acts in positioning the speed control devices 26, 27 for feed pumps 14, 15 respectively. Positioned in the divided pipe 63 are manual-automatic selector stations 69, 70 for remote manual speed control of either or both of the feed pumps.

Final steam temperature T2 (Fig. 1) is used as a low over-ride by way of a transmitter 7-1, pipe 72, standardizing relay 73 and starbup lock-out 74, eifective upon the B chamber of relay 58.

peratz'on-fl0w control (block load) This is a flow control to maintain a constant, predetermined fiow rate. The pump master selector station 59 would be turned to manual position cutting off communication with pipe 57 and manually establishing in pipe 75 a pressure representative of desired total feedwater supply rate. This loading pressure, acting through relay 53, is impressed upon the A chamber of relay 60. A loading pressure in pipe 65, representative of total water supply rate, is efifective upon the B chamber of relay 60 so that the output 68 will regulate the speed of pumps 14, 15 to maintain the desired flow regardless of changes in fluid coupling slippage, system resistance, etc. The desired total flow rate is established manually by the selector station 59 and against this loading is compared, as a checkback, a loading representative of actual flow rate. If there is a departure, in one direction or the other, then the loading in pipe 68 will regulate the speed of the pumps 14, 15 to correct until the actual rate of flow is the same as the desired rate of flow. This flow control apparatus and operation simplifies starting the second pump if a single pump is in use, since, with the first pump on auto matic, the control would unload the first pump automatically as the second pump is loaded manually.

Such flow control or block loading cannot change once it has been established by the master selector station 59. The flow control will hold to that rate. Variations in electrical load cannot change it and that selected feedwater flow rate establishes the firing rate to maintain final steam temperature. The turbine pressure governor is used as an unloading valve. If the unit loses the electrical end it trips 0d the boiler. If frequency falls there is no effect on the boiler. If there is a loss of firing it brings the unit down slowly.

Operation-pressure control (variable load) The second general possibility of control is operating on speed governing of the turbine and it will then be possible to put the pumps on pressure control by turning the master selector 59 to automatic. This will connect the pressure controller 50 and the load controller 52, by way of the pipe 57, with the flow total in pipe 65, so that the total fiow will vary automatically to keep up with changes in firing rate and turbine load. The control becomes one of operating the pumps in accordance with load (52), in accordance with throttle pressure (50), and with a checkback from measured total feedwater supply rate (65). The boiler pressure controller at the boiler outlet adjusts the feedwater pumps. The turbine valves set the load on the turbo-generator in accordance with requirements of the speed governor within limits as manually established. Turbine stage pressure as an indication of load or demand is used as an anticipator.

Operation-low temperature over-ride When operating on either scheme, the control incorporates a low temperature protective feature which will reduce flow on reduction of steam temperature so as to match water flow to firing rate. A second protective device is the low-flow unit trip 67 which will trip the unit in the event the control has reduced the flow rate below some 200,000 lb. per hr. either because of high pressure or low temperature.

During all normal operation the relay 73 subjects a loading pressure upon the B chamber of relay 58 which may be of an over-riding character. Start-up lock-out 74 is provided so that this low temperature over-ride can be removed from the system manually when it is not desired, for example during start-up and special emergency conditions, or for maintenance work.

The temperature standardizing relay 73 would be set so that its output will be zero when the steam temperature is above some predetermined value. When this output is zero, the master selector output (75) is repeated directly in the averaging relay 60 and calls for normal flow. If the temperature drops, the relay 73 output will go up and, in relay 58, will subtract a like amount from the selector 59 output so that the flow will be reduced. If the temperature levels off at the over-ride value, the control will hold the flow at that point, and if the temperature is restored, the flow will be brought back to its original value. If the temperature continues to drop below the over-ride point, the control will continue to reduce the flow down to a predetermined value, for example 200,000 lb. per hr., when the unit would be tripped.

Forced draft fan control While not shown on the drawings, it will be understood that the usual forced draft fan provisions are made for supplying combustion air to the duct 35 for distribution to the several cyclones. In Fig. 4 I show the load index pipe 53 joining a controller 76 to which forced draft duct pressure is also led. The controller 76 establishes in the pipe 77 a loading pressure which is applied to the A chamber of a standardizing relay 78. The output of the relay 78, acting through the manual-automatic selector station 79 provides a control pressure effective in positioning a motor or similar control device 80 for regulating forced draft fan speed. The load index, with checkback from actual duct pressure, regulates the supply of combustion air to the duct 35 to maintain the duct air pressure substantially constant but varying slightly with load as may be desired.

Heat input control Heat input to the unit is correlated with load, of which rate of feedwater supply is a close indication of rate of superheated steam discharged. The fuel and air supplied to all operating cyclones will be controlled basically and in direct proportion to the total feedwater flow, modified by intermediate zone steam temperature, and with a final control from superheated steam temperature. The combustion air to each individual cyclone is checked back by a measurement of air flow to that cyclone. The standard of each air flow control is modified as required to maintain a predetermined combustion gas analysis by means of a loading pressure from an oxygen recorder provided in connection with each cyclone.

Referring to Fig. 4 it will be seen that the loading pressures of pipe 66, representative of total water flow rate, is elfective within the A chamber of a relay 81 which receives in its B chamber a fluid loading pressure from pipe 82 continuously representative of intermediate zone temperature which may be at location T8, T9 or T10. While I have shown the possibility of using intermediate zone temperatures at T8, T9 or T10, it is to be under- '1 I stood that one only of these temperatures would be used and it would be selected during tune-up and calibration of the system. I show the three locations on Fig. l as exploratory temperatures to pick the one for incorporation in the system experimentally.

The relay 81 receives in its C chamber a loading pressure from pipe 83 the output of a standardizing relay 84 which receives in its A chamber the loading of the pipe 85 from final steam temperature T2 transmitter 71. Pipe 86 carries a control pressure resultant from the interrelation of the three mentioned loading pressures in relay 81, branching to manual-automatic selector stations 87, 88, 89 leading to the fuel feeder regulators 48-1, 48-2 and 48-3. At the same time (under automatic operation) the loading pipe 86 is effective through branch pipes 90, 91 and 92 upon the air control relays 93, 94 and 95.

Considering cyclone No. 'l as an example, the oxygen analyzer 25-1 establishes in a pipe 96 a fluid loading pressure which is applied to the C chamber of relay 93. At the same time the air measuring flow meter 37-1 establishes in a pipe 97 a fluid loading pressure effective upon the B chamber of a standardizing relay 98 whose A chamber receives the output of relay 93. The output of relay 98, effective through a pipe 99 and selector station 100 is elfective in positioning the damper 35-l regulating the supply of air to cyclone 1.

From this description it will be evident that the total coal supply, by way of the three feeders, as well as the total air supply, by way of the three air supplies, are simultaneously under the control of total water flow rate as an indication of rate of steam outflow, intermediate zone temperature as an anticipating efiect, and final steam temperature check-back as the desideratum to be attained. Simultaneously with this parallel fuel and air control there is a readjustment upon the air supply to each of the cyclones individually in accordance with a continuous determination of the free oxygen content of the gases discharged from that cyclone to the mixing chamber 4 and in accordance with a measurement of the actual rate of flow of air supplied to that cyclone as a check-back.

Under certain conditions of design and operation it may be desirable to arrange the heat supply in a somewhat different manner, for example, to have the readjustment applied to the coal feed rather than to the air supply rate. Thus, primary parallel control of fuel and air conjointly in accordance with total water flow rate, intermediate zone temperature, and final superheated fluid temperature; with measured air fiow to the individual cyclone readjusting that air supply rate, and with the oxygen anaylzer of each cyclone readjusting the related final supply rate.

Actual experience with a unit of this type has shown the interesting fact that final steam temperature reacted to drastic changes in flow pressure and firing rate initially in the wrong direction, but transition or intermediate zone temperature always started to swing immediately in the true direction of change. The reverse reaction of final steam temperature is explained by the variation of heat transfer coeifcient in a zone of more or less constant temperature (for the first short time at least). With constant heat input and a sudden reduction in flow the outlet temperature star-ts initially to drop because the lowered flow drops the outlet velocities and consequently the U value which reduces the temperature.

In describing the fuel and air supply control circuit of Fig. 4 it will be understood that control for the three cyclones is similar. I show the pipe 66 representative of total water flow rate extending ofi the right side of the drawing as well as a pipe 101 leading from a totalizing relay 192 and carrying an impulse representative of total air supply rate. The pipes 66 and 161 enter the left hand side of Fig. 4A to which reference may now be had for an explanation of control of recirculation of gases to the unit.

Recirculated gas control Referring to Fig. 4A it will be seen that the total mass gas flow meter 32 joins the B chamber of a relay 103 whose A chamber is joined selectively to either pipe 66 or pipe 161 in accordance with the selective hand actuated valve 104. Thus, in the relay 103, total gas fiow is continuously compared with total fresh air supply rate or total water flow rate, either one as an indication of load or demand. The discrepancy, if any, as an output pressure from relay 193, in pipe 105, is subjected upon the A chamber of relay 1&6 which receives in its B chamber a loading pressure representative of gas temperature taken at either location GT1 or GT2 (Fig. 1) as selected during initial placing in operation of the unit.

The resultant loading pressure in a pipe 167 is applied by way of a manual-automatic selector station to the controller 31 for regulating speed of the recirculating gas fan or fans. It will be understood that in certain installations the control may be used in positioning dampers rather than in controlling fan speed.

Fuel is burned and heat released as rapidly as possible, in a small hot space, to remove substantially all ash as molten slag. The cyclones discharge gases to the mixing chamber 4 at about 3100 F. Immediately the gas temperature is lowered to the order of 1900-2000 P. which is below the ash melting temperature and before the gases enter the small diameter closely spaced heating surfaces. The tempering is accomplished by diluting the fresh products of combustion with recirculated cooler gases, in general increasing the rate of recirculation with rating. Fig. 43 illustrates the general pattern of gas temperatures along the flow path, but the operating values may vary therefrom.

Thus, to accomplish this desideratum, I utilize a load index (either total water flow rate or total fresh air flow rate) in balance against total gas flow measure and with a check-back from an intermediate or reflecting gas temperature. The balance between the load index and the total gas flow is probably a constant percentage bias, although it may be otherwise arranged. The reason for using a temperature such as GT2 is due to the difiiculty of continuously and accurately measuring temperatures in the order of l900-2000 F. and therefore I go back into a cooler zone for a reflected temperature, Le, a temperature which reflects what is happening ahead or behind it in the gas flow path. On Fig. 4B I have shown the approximate locations of taking temperatures GT1 and GT2 to select the one which I desire to incorporate in the control of Fig. 4A.

Induced draft fan control Fig. 5 shows the type of control I apply to induced draft fan speed or dampers. This is in somewhat customary fashion but is shown to complete the disclosure of an operable unit. A furnace draft regulator ltlfi is continually sensitive to either positive or negative pressure within the furnace and establishes a fluid loading pressure in a pipe 109 representative thereof for positioning the controller 110.

Reheater outlet steam temperature control The unit is. designed to produce superheated steam leaving the high pressure reheater at 0' FTT and leaving the low pressure reheater at 1000 FTT at full load. Temperature of the low pressure reheater drops off faster than that of the high pressure reheater as load is reduced, due to the characteristics of such convection heating surfaces. Basic control of reheat temperatures, along with some control of primary steam total temperature, is provided for by gas proportioning over the parallel gas paths through the agency of dampers 38, 39. Since it is not feasible to control both reheat temperatures at the desired standard under all conditions, by manipulation of the gas distribution dampers alone, I have indicated the introduction of attemperation for each reheater as a supplemental feature.

The reheat temperature control arrangement as illus trated in Fig. 6 is based on control of the distribution dampers 38, 39 from the lower of the two reheat steam temperatures with the provision for automatic attemperation for the other reheater in case its discharge temperature tends to go above its desired standard. This is really a control from the reheat temperature which is to a greater extent below its standard value than is the other, because the two reheat temperatures do not have the same standard. In order to accomplish a selective control as to which is the lower, I provide a biasing of the effect from T6 so that the two temperature effects are as if they had the same standard, and then control from the lower of the two, bringing both up by gas flow distribution. This result is obtained by means of a selective relay which determines which of the two reheat temperature control impulses gets through to position the distribution dampers.

The high pressure reheat temperature transmitter T4 establishes a fluid loading pressure in a pipe 115 continuously representative of the value of T4 and of any departure from its standard of 1050 F. Similarly, the low pressure reheat temperature transmitter T6 establishes in a pipe 116 a fluid loading pressure continuously representative of the value of T6 and of any departure from its standard of 1000 F. The pipe 116 includes a calibrating relay 117 to bias the efiect to a value as if the standard for T6 were 1050 F., so that the resulting control efiect can be quickly compared with that in pipe 115. By way of example, if the pneumatic pressure in pipe 115 is 15 p.s.i. when the standard of 1050 F. for T4 exists and, for the same general adjustment the pressure in pipe 116 is 10 p.s.i. when the standard of 1000 F. for T6 exists, then the relay 117 will so modify, or amplify, the pressure of pipe 116 to bring it to a value of p.s.i. in pipe 118. Thus the selective relay 119 will continuously compare the pressure in pipe 115 with the biased pressure in pipe 118. For the example given there would be a pneumatic loading pressure of 15 p.s.i. subjected upon the A chamber of relay 119 and of 15 p.s.i. subjected upon the B chamber from pipe 118; when the desired standards of 1050 F. and 1000 F. for T4 and T6 respectively are had. Departure of either of the actual reheat outlet temperatures from its standard will change the pneumatic loading pressure in pipe 115 or in pipe 118 a proportionate amount from the standard value of 15 p.s.i.

Whichever of the two loading pressures, that of pipe 115 or that of pipe 118, is the lower indicates that the particular temperature T 4- or T6 has departed further in a lowering direction from its standard and that it is the pressure which is effective through output pipe 120, standardizing relay 121, and manual-automatic selector station 122, to position the gas distribution dampers 38, 39 in opposite directions by virtue of the reversing relay 123. If desired standard exists for both T4 and T6 then a loading pressure of 15 p.s.i. exists in the A and B chambers of relay 119 as well as in the D chamber and available in pipes 124, 125. Assume that the pressure in pipe 118 decreases to a value of 10 p.s.i. which is applied to the B chamber, this results in A chamber overbalancing B chamber to open communication between pipe 125 and the D chamber and the output pipe 120 to so control the gas distribution dampers 38, 39 as to pass more heating gases through the reheaters to bring the temperature of both up.

Conversely, if the pressure in pipe 115 is lowered to 10 p.s.i. while that in 118 remains at 15 p.s.i. then the B chamber overbalances the A chamber and a pressure of 10 psi. from pipe 124 is admitted to the D chamber and output pipe 120 again positioning the dampers 38, 39 in the same direction tending to raise both T4 and T6.

It will be understood that if, for example, T6 is the lower of the two and the above described operation occurs then both T6 and T4 will be raised and T4 might be raised above its design standard. For this reason, the

14 attemperator valves 113, 114 are available, controlling water to attemperators 111, 112 respectively (Fig. 1). Pipe 115 not only connects to the selective relay 119 but joins a standardizing relay 126 and manual-automatic selector station 127 for positioning the attemperator valve 113. In similar fashion pipe 118 joins standardizing re-v lay 128 and selector station 129 for positioning valve 114.

The standardizing relays 126 and 128 are adjusted to have a slightly higher set point than the relay 121. Accordingly, in the case of the temperature controller which shows the lowest temperature and is obtaining its increasing results from positioning of the gas distribution dampers, no attemperation will be called for as a rule. However, in the case of the other temperature controller, responsive to the other reheat temperature, which was not too low but may be raised to too high a value, the only means of control that it has access to is the attemperator valve to which it is connected, and if the steam temperature it is measuring tends to exceed the slightly higher standard mentioned above, attemperation will result.

While I have spoken of controlling the proportioning dampers from the lower (with respect to its optimum value) of the reheat temperatures this may be done by connecting the apparatus of Fig. 6 to control from the higher of the temperatures with respect to its optimum value.

Referring now to Fig. 7 I show therein in very schematic fashion a line drawing of the principal working medium paths through the universal pressure generator and the various turbines. A superheater by-pass pipe 23, with manual or remote manual shut-01f valve 24, allows the by-passing of certain convection superheating surfaces during start-up or other un-normal operating conditions. I show herein, very diagrammatically, pressure control for the turbine as well as steam cooling control for the high pressure turbine. These are shown to greater detail in Figs. 8 and 9 respectively.

Turbine pressure control In Fig. 8 the value P2 of conduit 17 is applied to the A chambers of standardizing relays 130 and 131. The output of relay 130 acts through a manual-automatic selector valve 132 to position a control valve 133 in the turbine by-pass conduit 134 leading to the deaerator or other feedwater storage and treating apparatus. At the same time, the output of relay 131 leads through the manual-automatic selector station 135 to a pressure governor 136. Shut-off, intercept, and similar valves are not shown in the system.

The turbine will be pressure governed normally so that its control valves act only to maintain 4500 p.s.i. at the turbine throttle. Conventional speed governing equipment will be provided so that it can either control the turbine or normally function as an over-riding control on the pressure governor. The pressure controller would be set up to control the turbine throttle pressure either by operating the turbine throttle valves or the turbine by-pass valve, selectively, or, possibly, both simultaneously. Relay 130 and selector station 132 will operate the turbine by-pass valve 133. The other relay 131 and its station "135 will supply loading pressure to the turbine pressure governor 136 (very diagrammatically) which will operate the turbine throttle valves in accordance with the control signal. The turbine throttle valve selector station 135 is provided with a remote set point adjustment 137 so that the controller could also function as an initial pressure regulator when operating the turbine on speed control.

There may possibly be a drop in steam temperature when the turbine is on speed governing. Under this condition the initial temperature regulator will reduce flow to maintain steam temperature at the same time the turbine will call for more steam. Initial temperature regulator would over-ride and the turbine would run at a throttled condition probably necessitating a load cut. If the temperature continued to drop the flow would be reduced until the unit was removed from service by the low flow trip 67 (Fig. 4).

Inasmuch as it is not desirable to pass extremely high temperature steam through the by-pass line 134, by way of valve 133, to the deaerating or other feedwater treating equipment I have shown an attemperator 138 in the steam line 134. The attemperator is supplied with water through a pipe 139 under the control of a valve 140 and temperature controller 141.

Turbine cooling steam control In Fig. 9 I show a larger detail control of turbine cooling steam which is taken from the main supply pipe 142. In other words, this is a portion of the total steam supplied to the high pressure turbine and is to vary somewhat with load.

It is expected that the cooling steam requirement will vary from 40,000 to 100,000 lb. per hr. depending somewhat on the final design of the turbine. A most suitable source is to take the final steam and attemperate it down to the desired temperature. The cooling steam supply will be taken from the main steam leads on the turbine side of the control valves. There may be valves in the branch line 143, or the flow may be set by orifices such as 144 at points of admission to the turbine. The quantity of cooling steam will remain a fixed percentage of throttle flow and will be proportional to load. Attemperator water is supplied through a pipe 145, to the attemperator 146, under control of a regulating valve 147 and is taken from the boiler feed line.

The control valve 147 receives a primary impulse from position transmitter 148, acting through standardizing relay 149, modified by an impulse from the steam temperature sensitive transmitter 151} sensing attemperated steam temperature. As a check-back the water flow transmitter 151 is sensitive to rate of attemperating water passing through the pipe 145 and initiates an impulse effective in the relay 14?. The output of the relay 149 joins a relay 152 receiving the impulse from transmitter 150 by way of a standardizing relay 153. Output of relay 152 is effective, through a manual-autor1na7tic selector station 154, in positioning control valve M anu'al control Referring to Fig. 3 it will be observed that I have shown a measuring-control panel to provide instrumentalities and remote control possibilities for performing the methods of my invention manually-remotely. The dotted upper section 169 may represent the vertical portion of a panel board upon which are mounted indicating and/or recording instruments of the various measured variables previously discussed. The lower dotted portion 161 may be in the form of a bench or console type control section and contains the necessary start-stop-reverse push button stations in connection withspeed varying rheostats (where applicable) for remotely manually positioning the controlled agents or variables to perform manually the methods which the apparatus of figures previously described will automatically perform. Below the control portion of the board 161 I show the various motor (M) blocks for positioning dampers and the like. For example, the feed pumps 14, '15 are'under control of motive means whose speed controls 26, 27 are shown on the control board 161.

The control systems described are of the pneumatic fluid pressure actuated type and the various control devices or actuators take the form of pneumatically powered motors. The motors M of Fig. 3, for positioning dampers etc., may be pneumatically actuated remotely or may be electrically actuated, as indicated by the push buttons and rheostats of panel portion 161.

Although I have chosen to illustrate and describe in some detail a certain size and type of power station, it will be understood that this is not limiting, except as to the claims which may be allowed.

What I claim as new, and desire to secure by Letters Patent of the United States, is:

l. The method of operating a forced-flow once through above-critical pressure vapor generator having a primary furnace chamber, means for burning fuel at high heat release rates in said primary furnace chamber, a mixing chamber receiving the products of combustion from the primary furnace chamber as well as tempering gases recirculated from a location beyond at least a portion of the heat absorption surfaces of the unit, a tubular pressure flow path for the working medium receiving at one end liquid substantially above its critical pressure and discharging superheated fluid from its other end, the tubular flow path serially forming at least one boundary wall of the primary furnace chamber then radiant wall portions of the mixing chamber, then convection superheater surface in the gas path after the mixing chamber; which includes, regulating the liquid supply rate to the input end of the tubular flow path in response to fluid pressure at the exit of the path in direction tending to increase the liquid supply rate or pressure as exit fluid pressure decreases and vice versa, and controlling the firing of the primary furnace chamber in response to final superheater fluid temperature in direction tending to increase the firing rate as final fluid temperature decreases and vice versa.

2. The method of operating a vapor generator of the type defined in claim 1 which includes, regulating the liquid supply to the input end of the tubular flow path in direct response to an indication of load upon the unit.

3. The method of claim 1 wherein the regulation of liquid supply tothe input end of the fluid flow path is conjointly in inverse response to fluid pressure at the exit of the path, in direct response to an indication of load upon the unit, and in inverse response to a measure of the total fluid supply rate.

4. The method of operating a vapor generator of the type defined in claim 1 which includes, regulating the liquid supply to the input end of the tubular flow path in inverse response to fluid pressure at the exit, and controlling the firing of the primary furnace chamber in inverse response to final superheated temperature and in direct response to measured total liquid supply rate.

5. The method of operating a forced-flow once-through above-critical pressure vapor generator having a plurality of primary furnace chambers, means for burning fuel at high heat release rates in the primary furnace chambers, a mixing chamber receiving the products of combustion from the primary furnace chambers as well as tempering gases recirculated from a location beyond at least a portion of the heat absorption surfaces of the unit, separately controllable fuel and air supplies to each of the primary furnaces, a tubular pressure flow path for the working medium receiving at one end liquid substantially above its critical pressure and discharging superheated fluid from its other end, the tubular flow path serially forming at least one boundary wallof each of the primary furnace chambers then radiant wall portions of the mixing chamber then convection superheating surface in the gas flow path after the mixing chamber; which includes, regulating the liquid supply rate to the input end of the tubular flow path in accordance with fluid pressure at the exit of the path; controlling total fuel and air supply rates for combustion to the primary furnace chambers in parallel in conjoint response to a measure of rate of flow of fluid through the tubular path, final superheated fluid temperature, and an intermediate zone fluid temperature; readjusting the air supply rates to the primary furnace chambers in accordance with measurement of the total of the individual air supply rates, and readjusting if necessary the fuel supply rate to each primary furnace chamber individually in accordance with an analysis of the products of combustion discharged by that furnace chamber to the mixing chamher.

6. The method of claim 1 including regulating rate of tempering gas recirculation to the mixing chamber generally directly in accordance with unit demand, and readjusting recirculation rate conjointly responsive to rate of total heating gas mass flow over the convection surfaces and to a measurement of gas temperature at a selected location along the heating path of convection surfaces, the readjustment being generally inversely with both mass flow and gas temperature. 7 p

7. The method of operating a forced-flow once-through vapor generator having a primary furnace chamber, means for burning fuel at high heat release rates in said primary furnace chamber, a mixing chamber receiving the products of combustion from the primary furnace chamber as well as tempering gases recirculated from a location beyond at least a portionof the heat absorption surfaces of the unit, a tubular pressure flow path for the working medium receiving at one end liquid under substantial pressure and discharging superheated fluid from its other end, the tubular flow path serially forming at least one boundary wall of the primary furnace chamher then radiant wall portions of the mixing chamber then convection superheater surface in the gas path after the mixing chamber; which includes, regulating the liquid supply rate to the input end of the tubular flow path in accordance with fluid pressure at the exit of the path in direction tending to increase the liquid supply rate or pressure as exit fluid pressure decreases and vice versa, supplying the elements of combustion to the primary furnace chamber in accordance with final superheated fluid temperature in direction tending to increase the supply rate as final fluid temperature decreases and vice versa, recirculating partially cooled heating gases from beyond at least a portion of the convection heating surfaces to the mixing chamber to temper therein the products of combustion supplied by the primary furnace chamber, and regulating the recirculation in direction to increase the rate of recirculation as load increases.

8. The method of operating a thermal power plant including a forced-flow once-through above-critical pressure heater comprising a heated tubular flow path for the working medium receiving at one end liquid substantially above its critical pressure and discharging superheated fluid from its other end to a utilizer, means for burning fuel at high heat release rates in a primary furnace of the heater, a mixing chamber receiving the products of combustion from the primary furnace as well as tempering gases recirculated from a location beyond at least a portion of the heat absorption surfaces of the unit, the tubular flow path serially forming at least one boundary wall of the primary furnace then radiant Wall portions of the mixing chamber then convect-ion superheating surface in the gas path after the mixing chamber, convection reheat surface for the fluid leaving the utilizer which is in a separate heating gas flow path parallel to the convection superheating portion of the tubular path, which includes; regulating the liquid supply rate to the inlet end of the tubular flow path in accordance with pressure of the fluid supplied the utilizer, controlling the firing of the primary furnace in accordance with total temperature of the fluid supplied the utilizer, regulating the rate of gas recirculation directly in proportion to load, and proportioning the heating gas flow between the convection superheating surface and the convection reheating surface in accordance with final reheated fluid temperature.

9. Apparatus for controlling the operation of a forced- 18 flow once-through above-critical pressure vapor generator having a primary furnace chamber supplied with fuel and air for combustion and having a mixing chamber to which the products of combustion are discharged and from which heating gases pass over convection heating surfaces and having a tubular pressure fluid flow path for the working medium receiving at one end liquid substantially above its critical pressure and discharging superheated fiuid from its other end, the tubular flow path forming at least one boundary wall of the primary furnace chamber then radiant wall portions of the mixing chamber then convection superheater surface in the gas pass after the mixing chamber, in combination, pressure determining means of the fluid at the exit of the heated path, pump means supplying liquid under substantial pressure to the inlet of said path, means regulating the pump means and responsive to said pressure determining means, the regulating means tending to so regulate the pump means as to increasethe liquid supply rate or pressure as exit fluid pressure decreases and vice versa, temperature determining means of the fluid at the exit of the heated path, and means controlling the supplying of fuel and air for combustion, responsive to said temperature determining means, the controlling means tending to increase the supply rate'of fuel and air for combustion as finalfluid temperature decreases and vice versa.

10. Apparatus for controlling the operation of a forcedflow once-throughabovecritical pressure vapor generator having a primary furnace chamber discharging products of combustion to a mixing chamber from which heating gases pass over convection heating surfaces and having a tubular pressure fluid flow path for the working medium receiving at one end liquid substantially above its critical pressure and discharging superheated fluid from its other end, the tubular flow path forming at least one boundary wall of the primary furnace chamber then radiant wall portions of the mixing chamber then convection superheater surface in the gas pass after the mixing chamber, in combination, pressure determining means of the fluid at the exit of the heated path, pump means supplying liquid under substantial pressure to the inlet of said path, means regulating the pump means and responsive to said pressure determining means, controllable separate fuel and air supply apparatus for the primary furnace chamber, a meter of fluid flow rate through the tubular path, temperature determining means of the fluid at the exit of the path, a measuring device sensitive to fluid temperature at a selected intermediate zone of the tubular path; control means responsive to said meter, temperature determining means and device adapted to control both fuel and air supplies in parallel to the primary furnace chamber; metering means determining supply rate of the air, a gas analyzer of the products of combustion entering the mixing chamber from the primary furnace chamber, and readjusting means for the air supply rate responsive to the said metering means and gas analyzer.

11. Apparatus for controlling the operation of a forcedflow once-through above-critical pressure vapor generator having a plurality of primary furnace chambers each supplied with fuel and air for combustion and discharging products of combustion to a mixing chamber which also receives tempering gases recirculated from a location beyond at least a portion of the heat absorption surfaces of the unit, from which heating gases pass over convection heating surfaces and having a tubular pressure fluid flow path for the working medium receiving at one end liquid substantially above its critical pressure and discharging superheated fluid from its other end, the tubular flow path forming at least one boundary wall of each of the primary furnace chambers then radiant wall portions of the mixing chamber then convection superheater surface in the gas pass after the mixing chamber, in combination, pressure determining means of the fluid at the exit of the heated path, pump means supplying liquid .under substantial pressure to the inlet of said path, means regulating the pump means and responsive to said pressure determining means, controllable separate fuel and air supply apparatus for each of the primary furnace chambers, a meter of fluid flow rate through the tubular path, temperature determining means of the fluid at the exit of the path, a measuring device sensitive to fluid temperature at a selected intermediate zone of the tubular path; control means responsiveto said meter, tem- 'perature determining means and deivce adapted to control both fuel and air supplies in parallel to the several furnace chambers; and for each of the primary furnaces separately, metering means determining the rate of supply of an element of combustion to that primary furnace chamber, a gas analyzer 013- the products of combustion entering the mixing chamber from that primary furnace chamber before tempering dilution, and readjusting means for the supply rate of one of the elements of combustion to that primary furnace chamber responsive to the said metering means and gas analyzer.

12. The apparatus of claim 9 including fan and duct means arranged to recirculate partially cooled heating gases from beyond at least a portion of the convection heating surfaces back to the mixing chamber, unit demand responsive means arranged in connection with said fan and duct means to regulate recirculation rate generally in direct accordance with demand, a meter of total heating gas mass flow over the convection heating surfaces, a device measuring gas temperature at a selected location along the heating path of convection surfaces, and means readjusting if necessary the recirculation rate conjointly responsive to said device and last named means and generally in an inverse direction.

13. The apparatus of claim 9 including fan and duct means arranged to recirculate partially cooled heating gases from beyond at least a portion of the convection heating surfaces back to the mixing chamber, a measuring device of total combustion air supply rate to the unit, a meter of total heating mass flow rate over the convection heating surfaces, and control means for said gas vrecirculating means in conjoint response inversely with said measuring device and directly with said meter.

14. The apparatus of claim 9 including fan and duct means arranged to recirculate partially cooled heating gases from beyond at least a portion of the convection heating surfaces back to the mixing chamber, flow rate means continuously measuring rate of flow of fluid through the tubular heating path as an indication of load arranged to control the gas recirculating means to generally proportion recirculated gas to demand, a meter of total heating mass flow rate over the convection heating surfaces, means measuring gas temperature at a selected location along the heating path of convection surfaces, and regulating means readjusting if necessary the recirculation rate conjointly responsive to said last named meter and gas temperature measuring means and acting in general inverse direction with relation to demand.

15. Apparatus for controlling the operation of a forcedflow once-through vapor generator having a primary furnace chamber supplied with fuel and air for combustion and having a mixing chamber to which the products of combustion are discharged and which also receives tempering gases recirculated from a location beyond at least a portion of the heat absorption surfaces of the unit, from which heating gases pass over convection heating surfaces and having a tubular pressure fluid flow path for the working medium receiving at one end liquid under substantial pressure and discharging superheated fluid at its other end, the tubular flow path serially forming at least one boundary wall of the primary furnace chamber then radiant Wall portions of the mixing chamber then convection superheater surface in the gas path after the mixing chamber, in combination, means regulating liquid supply rate to the input end of the tubular path continuously in inverse response to a measurement of fluid pressure at the path exit, means regulating fuel and air supply rate to the primary furnace chamber continuously in inverse response to a measurement of final superheated fluid temperature, fan and duct means arranged to recirculate partially cooled heating gases from beyond at least a portion of the convection heating surfaces back to the mixing chamber to temper therein the products of combustion supplied thereto by the primary furnace chamber, and means regulating the rate of recirculation in direction to increase the recirculation rate as load increases.

16. Apparatus for controlling the operation of a forced flow once-through vapor generator having a plurality of primary furnace chambers supplied with fuel and air for combustion and having a mixing chamber to which the products of combustion are discharged and which also receives tempering gases recirculated from a location beyond at least a portion of the heat absorption surfaces of the unit, from which heating gases pass over convection heating surfaces and having a tubular pressure fluid flow path for the working medium receiving at one end liquid under substantial pressure and discharging superheated fluid at its other end, the tubular flow path serially forming at least one boundary wall of each of the primary furnace chambers then radiant wall portions of the mixing chamber then convection superheater surface in the gas path after the mixing chamber, in combination, means regulating liquid supply rate to the input end of the tubular path continuously in inverse response to a measurement of fluid pressure at the path exit, means regulating total fuel and air supply rates to the primary furnace chamber in parallel continuously in direct response to a measure of rate of fluid flow through the tubular path, in inverse response to a measurement of final superheated fluid temperature and in inverse response to a determination of fluid temperature in an intermediate zone between the ends of the fluid path; fan and duct means arranged to recirculate partially cooled heating gases from beyond at least a portion of the convection heating surfaces back to the mixing chamber to temper therein the products of combustion supplied thereto by the primary furnace chambers, and means regulating the rate of recirculation in direction to increase the recirculation rate as load increases.

17. Apparatus for controlling the operation of a thermal power plant including a forced-flow once-through above-critical pressure heater having a heated tubular flow path for the working medium receiving at one end liquid substantially above its critical pressure and discharging superheated fluid from its other end to a utilizer, means for burning fuel at high heat release rates in a primary furnace of the heater, a mixing chamber receiving the products of combustion from the primary furnace as well as tempering gases recirculated from a location beyond at least a portion of the heat absorption surfaces of the unit, the tubular flow path serially forming at least one boundary wall of the primary furnace then radiant wall portions of the mixing chamber then convection superheating surface in the gas path after the mixing chamber, convection reheat surface for the fluid leaving the utilizer which is in a separate heating gas flow path parallel to the convection superheating portion of the tubular path, including in combination, pump means supplying liquid to the tubular path in response to a measurement of pressure of the fluid supplied to the utilizer, a controllable supply of the elements of combustion for the furnace, control means for said supply means sensitive to total temperature of the fluid supplied the utilizer, fan and duct means arranged to recirculate partially cooled heating gases from beyond at least a portion of the superheating surfaces back to the mixing chamber, means regulating the rate of gas recirculation directly in proportion to load, damper means arranged to proportion the heating gases over the superheating and reheating surfaces, a measuring device of the final reheated fluid temperature, and regulating means for the damper means responsive to said last named measuring device.

18. A control system for a supercritical pressure boiler comprising means to supply fuel and air for combustion to the boiler, pump means to force water into the boiler at a supercritical pressure, an outlet conduit for steam at supercritical pressure from the boiler, control means responsive to the pressure of steam in the outlet conduit to control the flow of water to the boiler, control means instantaneously and proportionately responsive to the demand for steam from the boiler to control the supply of fuel and air to the boiler, and control means responsive to the temperature of the steam in the outlet conduit to modify control of at least one of said supplies at a slower rate than the control is efiected by the demand responsive means.

19. A control system for a supercritical pressure boiler comprising means to supply fuel and air for combustion to the boiler, pump means to force Water into the boiler L at a supercritical pressure, an outlet conduit for steam at supercritical pressure from the boiler, first control means responsive to the pressure of steam in the outlet conduit to control the flow of water to the boiler, means responsive to the temperature and flow of the steam in the outlet conduit to modify the effect of said first control means, and second control means responsive to the demand for steam from the boiler to control the supply of fuel and air to the boiler.

20. A control system for a supercritical pressure boiler comprising means to supply fuel and air for combustion to the boiler, pump means to force Water into the boiler at a supercritical pressure, an outlet conduit for steam at supercritical pressure from the boiler, control means responsive to the pressure of steam in the outlet conduit to control the flow of water to the boiler, means responsive to the temperature of the steam in the outlet conduit to modify the effect of said control means, control means responsive to the demand for steam from the boiler to control the supply of fuel and air to the boiler and a connection from the temperature responsive modifying means to the last named control means to modify the control of at least one of said supplies at a slower rate than the control is effected by the flow responsive means.

21. A control system for a supercritical pressure boiler comprising means to supply fuel and air for combustion to the boiler, pump means to force Water into the boiler at a supercritical pressure, an outlet conduit for steam at supercritical pressure from the boiler, control means responsive to the pressure of steam in the outlet conduit to control the flow of water to the boiler, control means responsive to flow of steam through the outlet conduit to control the supply of air to the boiler, and control means jointly responsive to flow of steam through the outlet conduit and to temperature of steam in the outlet conduit to control the supply of fuel to the boiler.

22. In a control system for a supercritical pressure boiler, means to force water into the boiler at supercritical pressure, an outlet conduit to conduct steam from the boiler, control means responsive to the pressure of steam in the outlet conduit to control the forcing means, means responsive to the demand for steam from the boiler to produce a first controlling force, means responsive to said controlling force to control the rate of firing of the boiler, means responsive to the temperature of the steam in the outlet conduit to produce a second controlling force, means connected to the temperature responsive means and the demand responsive means and operating to combine the controlling forces to modify control of the firing rate in response to changes in steam temperature, and means connecting the temperature responsive means to the first named control means to modify control of the water forcing means in accordance with steam temperature.

References Cited in the file of this patent UNITED STATES PATENTS 1,562,087 Griswold Nov. 17, 1925 1,599,410 Gilooly Sept. 14, 1926 1,726,561 Hodgkinson et al. Sept. 3, 1929 1,884,897 Smith Oct. 25, 1932 1,887,536 Baumann et a1 Nov. 15, 1932 1,975,086 Dickey Oct. 2, 1934 1,975,104 Junkins Oct. 2, 1934 2,052,375 Wunsch et al. Aug. 25, 1936 2,081,948 Michel et al. June 1, 1937 2,095,991 Lysholm Oct. 19, 1937 2,229,643 DeBaufre Jan. 28, 1941 2,298,257 Reaser et al. Oct. 6, 1942 2,357,301 Bailey et al. Sept. 5, 1944 2,594,312 Kerr et al. Apr. 29, 1952 2,602,433 Kuppenheimer July 8, 1952 2,649,079 Van Brunt Aug. 18, 1953 2,685,280 Blaskowski Aug. 3, 1954 2,804,851 Smoot Sept. 3, 1957 FOREIGN PATENTS 398,413 Great Britain Sept. 14, 1933 719,986 Great Britain Dec. 8, 1954 

